Life tables are presented from six field populations of first- and second-generation southwestern corn borer,Diatraea grandiosellaDyar, infesting corn during a 3-yr study in the Texas High Plains. Survival from egg to adult was greater for first (0.20–0.52) than second (0.007–0.038) generation. Key-factor analysis identified egg mortality during first generation and large larval and diapausing larval mortality during the second generation as largely responsible for observed changes in generation survival. Stage-specific mortality for the first generation was predominately density-independent, and only negligible mortality was caused by natural enemies and intraspecific competition. Density-dependent mortality occurred in large larvae during the second generation. Intraspecific competition (cannibalism) and infection byBeauveria bassiana(Balsoma) Vuillemin were major second-generation mortality factors for large larvae and apparently were responsible for the observed density-dependent mortality. Adults developing from first-generation larvae on whorl-stage corn were significantly more fecund than second-generation adults developing as larvae on post-tassel-stage corn. The net reproductive rate was considerably greater during the first (Ro = 95) than second (Ro = 4) generation. Management tactics are proposed for reducing the economic effect of second-generation southwestern corn borer by suppressing the first-generation population increase.